Rick Santorum won crucial primaries in Alabama and Mississippi in the race for the Republican presidential nomination, dealing a devastating blow to Newt Gingrich and securing his position as the chief conservative alternative to front-runner Mitt Romney.

Tuesday's results were a setback for Romney, who had hoped to show he could muster the support of evangelical Christian voters in America's Deep South in his quest to be his party's choice to challenge President Barack Obama in November's election.

But they were especially bad news for Gingrich, who desperately needed a win to show he remains a viable candidate.

"We did it again," Santorum exulted before cheering supporters in Lafayette, Louisiana, which holds its primary March 24. He said it was time for conservatives to unite in an effort to defeat Romney. Gingrich said he had no plans to leave the race.

In Alabama on Tuesday night, with 97 percent of the precincts counted, Santorum had 35 percent of the vote, while Gingrich and Romney each had 29 percent.

Returns from 99 percent of Mississippi's precincts showed Santorum with 33 percent, Gingrich 31 percent and Romney 30 percent.

The fourth candidate, Texas Rep. Ron Paul, did not compete actively in the two contests and lagged far behind in single digits.

On Wednesday, Mitt Romney won the caucuses in Hawaii and added a sweep of delegates from Republican nominating caucuses in American Samoa.

Romney still holds a commanding lead in delegates to the convention in Tampa, Florida, in August. The former Massachusetts governor is much better funded and has a superior campaign organization. What's more, he carries the backing of the party establishment. But the conservative base distrusts his one-time moderate views on important social issues like abortion and gay rights.

Slower still to fall in behind Romney have been voters in the Deep South, where he has yet to win a primary. He won in Virginia, where Santorum and Gingrich failed to qualify for the ballot, and in Florida, where he carried counties with many transplanted retirees from northern states but lost those regions in northern Florida most culturally aligned with the old South.

Romney congratulated Santorum in a written statement, but noted that "with the delegates won tonight, we are even closer to the nomination."

Romney's allies say the candidate's steady collection of delegates to the Republican National Convention makes it almost impossible for his rivals to catch up to him. But revised party rules, which allow many states to allocate delegates proportionally instead of winner-take-all, make it difficult for Romney to secure the delegates he needs to secure the nomination before mid-summer, if then.

A win in either Mississippi or Alabama would have eased concerns that the Harvard-educated Mormon cannot win over the party's most conservative and evangelical Christian voters. In both states, 80 percent or more of voters leaving their polling places said they were born again Christians or evangelicals. Exit polls showed an electorate that is conservative, determinedly Republican and profoundly unhappy about the government.

The numbers spelled good news for Santorum, a former Pennsylvania senator and deeply conservative Catholic who has captured the hearts of his party's base.

"People of Mississippi and Alabama want a conservative," Santorum told reporters in Biloxi, Mississippi, before the results were tallied, pressing his argument that Gingrich should consider stepping aside. "If they want a conservative nominee for sure, they can do that by lining up behind us and making this race clearly a two-person race outside of the South."

The survival of Gingrich's campaign had essentially rested on winning both of Tuesday's contests. The former speaker of the House of Representatives has pursued an all-Southern strategy, but he has won only South Carolina and Georgia, the state he represented in Congress for 20 years.

He congratulated Santorum on his victories, and poked fun at Romney. "If you're the front-runner and you keep coming in third, you're not much of a front-runner," he said in Birmingham, Alabama.

There were 107 Republican National Convention delegates at stake on Tuesday: 47 in Alabama, 37 in Mississippi, 17 in Hawai and six more in American Samoa.

Santorum's two victories were worth at least 29 delegates. Gingrich won at least 24 and Romney at least 22. The split in Mississippi underscored the difficulty that Romney's rivals face in overcoming his big lead. Santorum garnered 13 delegates, while Gingrich and Romney each had 12 delegates.

Romney also won Tuesday's Republican caucus in American Samoa, picking up the six delegates selected at the meeting and pledges of support from the Pacific island nation's three superdelegates.

The partial allocation of delegates from the primary states left Romney with at least 482 in The Associated Press count, out of the 1,144 needed to win the nomination. Santorum had 246, Gingrich 131 and Paul 47.

Santorum and Romney planned to campaign in the next few days in Puerto Rico, which holds a primary on Sunday. Twenty-three delegates are at stake in the U.S. territory.

The showdown primaries occurred as new polling showed a steep drop in Obama's approval ratings, a decline that coincides with rapidly climbing gasoline prices as a result of renewed turbulence in the Middle East. The political turmoil across the Mideast and North Africa has been exacerbated by fears that Israel is preparing a military attack on Iran's suspected nuclear weapons program.

A Washington Post-ABC News poll found that 46 percent of those surveyed approve the way the president is handling his job, and 50 percent disapprove. A New York Times/CBS poll nd 41 percent approval, and 47 percent disapproval.

Leavening those numbers, the Gallup daily tracking poll had Obama's approval rating at 47 percent. It showed U.S. ┬Čeconomic confidence at a four-year high.

On Tuesday, the president, who is unopposed for the Democratic nomination, won the endorsement of the AFL-CIO labor federation